System for eliminating gases in a container

ABSTRACT

Apparatus for removing gases from a container used to prepare concentrates of a powder in water are disclosed including a supply conduit for supplying water to the container, a removal conduit for removing the concentrate from the container, a pump including a negative pressure side, an evacuation conduit for connecting the negative pressure side of the pump with the container, an actuatable valve disposed in the evacuation conduit whereby upon actuation the actuatable valve connects the container with the negative pressure side of the pump, an indicator for indicating when the container includes a predetermined amount of the gases, and a control mechanism for actuating the valve in response to the indicator to eliminate the gases from the container.

This application is a 371 of PCT/SE97/00593, filed on Apr. 10, 1997.

FIELD OF THE INVENTION

The present invention relates to an improvement in a dialysis machine ofthe type which is described in European Patent No. 278,100 whichcorresponds to the dialysis machine known as GAMBRO AK 100.

BACKGROUND OF THE INVENTION

In a dialysis machine of the above-mentioned type, one or morecartridges containing sodium bicarbonate powder, sodium chloride orother salts are used. The salt is dissolved by the introduction of waterinto the cartridge and removal of concentrate from the cartridge. Theconcentrate is used to prepare the intended dialysis solution.

The composition of the dialysis solution is determined in the dialysismachine by measuring the conductivity of the prepared solution andregulating dosage pumps for each of the various concentrates. It is nowcommon to use two different concentrates; a B-concentrate comprisingonly bicarbonate from the above-mentioned bicarbonate cartridge, and anA-concentrate comprising the remaining components in concentrated form,for example to a 37-fold concentration. Other combinations ofconcentrates also exist, such as the B-concentrate, which besidesbicarbonate, may also comprise sodium chloride. Alternatively, theB-concentrate can be divided into two parts comprising bicarbonate andsodium chloride, respectively, whereby the A-concentrate comprises theremaining components in a more concentrated form.

By preparing the bicarbonate concentrate and, where appropriate, thesodium chloride concentrate on demand in the dialysis machine, anadvantage is realized in that the bicarbonate concentrate remains stableuntil it is used in a dialyser connected to the dialysis machine.

If a dialysis solution is prepared in advance, which is also now acommon procedure, the risk exists that the bicarbonate can decompose tocarbon dioxide and carbonate. This implies that the pH value for thesolution rises and the risk of precipitation of the calcium carbonatearises during mixing to the prepared dialysis solution. This can affectthe final composition of the dialysis solution (reduction of the calciumion concentrate) as well as creating problems of silting up of conduitsand components in the dialysis machine due to the deposition of calciumcarbonate. For these reasons, the bicarbonate cartridge as describedabove has attained widespread use.

As mentioned above, the dialysis solution is prepared by mixing the twoconcentrates with water. The mixing process is regulated by conductivitymeters which control various dosage pumps. Conductivity meters are,however, sensitive to possible incorporation of gas bubbles in thesolution. Thus, the conductivity meters are generally preceded by gasseparators whereby more accurate, less fluctuating measuring values canbe obtained.

The dialysis machine is provided with a monitoring system which isseparated from the regulating system and serves to emit alarm signalsshould error situations arise. In the above-mentioned dialysis machine;namely, GAMBRO AK 100, monitoring of the dosage of concentrate occurs bymonitoring the number of revolutions of the dosage pumps. If the numberof revolutions differs too greatly from an expected value, an alarmsignal is emitted.

When using the above-mentioned bicarbonate cartridge containing drybicarbonate powder, it is necessary that the powder be wetted with waterprior to use. This takes place in a particular "priming step". Water isintroduced into the cartridge at its upper end at the same time that asubstantial vacuum is applied to the lower end of the cartridge. Waterthus fills substantially the entire cartridge in less than a minute.

When a sensor positioned downstream of the bicarbonate cartridge detectsthat primarily concentrate is flowing from the cartridge, the sensorindicates that the priming step is complete. A valve then switches overthe machine so that the substantial vacuum is terminated. This sensorcan be the above-mentioned conductivity meter.

During the priming step, a small quantity of air or gas is normallytrapped at the upper end of the cartridge. This quantity of gas doesnot, however, normally affect the functioning of the cartridge. In theabove-mentioned European Patent No. 278,100, various methods aredescribed for removing this quantity of gas before the dialysistreatment commences, i.e. during the priming step.

However, it sometimes occurs that the trapped gas in the upper region ofthe cartridge increases in volume during the dialysis treatment. If thetrapped volume of gas becomes so great that a considerable quantity ofgas passes out through the outlet of the cartridge and reaches theconductivity meter, an alarm is raised. Furthermore, it will beappreciated that the normal functioning of the cartridge is greatlyaffected if far too great a volume of gas is present in the cartridge.Normally, it is preferred that the water level always remains above thesalt particle level in the cartridge.

The above-mentioned condition with increasing volume of gas can beattributed to several causes. One possible cause is leakage in theconnection between the upper or lower ends of the cartridge and thedialysis machine. The dialysis machine normally maintains a small vacuumin the cartridge. Another such cause can be that gas bubbles accompanythe water which enters the cartridge and thereafter become separated inthe cartridge. The principal cause would seem, however, to be gasformation in the cartridge, such as formation of carbon dioxide gas.

It has been observed that the above-mentioned problem is exacerbated athigher ambient temperatures, which is probably due to the decompositionof bicarbonate to carbon dioxide and carbonate.

Since the cartridge circuit is closed, there is no other route for thegas to flow than through the outlet from the cartridge, something whichcan activate the above-mentioned conductivity alarm. In order to dealwith such an alarm situation, it is then necessary to remove thebicarbonate cartridge and to insert a new cartridge into the system,whereafter the machine has to be restarted with a priming step andsubsequent stabilising steps, something which can take a long period oftime. During this time, the dialysis treatment has to be interrupted.

It has also been observed that the conductivity signal from theconductivity meter, despite the preceding gas situation, fluctuatesgreatly, particularly at high ambient temperatures. In extreme cases,such as at high temperatures, these fluctuations are so great that thealarm limit is exceeded.

It is noted that Japanese Patent No. 55115819 describes a method ofdegassing the water, and also possibly the concentrates, prior to mixingat volumetric dilution in order to avoid problems relating to airbubbles being formed during heating.

SUMMARY OF THE INVENTION

One object of the present invention is to provide a system whichovercomes the above-mentioned problems associated with gas-filling in abicarbonate cartridge.

Another object of the present invention is to provide an indicatingarrangement for indicating when a dialysis cartridge runs the risk ofbecoming full of gas and measures are required in order to remove thisgas.

A further object of the present invention is to improve the priming of adialysis cartridge.

In accordance with the present invention, these and other objects havenow been realized by the discovery of apparatus for the elimination ofgases from a container including an upper end and a lower end forpreparing a concentrate of a powder in water, the apparatus comprising asupply conduit for supplying water to the container, a removal conduitfor removing the concentrate from the container, a pump including anegative pressure side, an evacuation conduit for connecting thenegative pressure side of the pump with the container, an actuatablevalve disposed in the evacuation conduit whereby upon actuation saidactuatable valve connects the container with the negative pressure sideof the pump, an indicator for indicating when the container includes apredetermined amount of the gases, and control means for actuating thevalve in response to the indicator to eliminate the gases from thecontainer. In accordance with a preferred embodiment, the powdercomprises a bicarbonate powder and the concentrate comprises a dialysissolution.

In accordance with one embodiment of the apparatus of the presentinvention, the actuatable valve comprises a three-way valve normallyconnecting the supply conduit to the upper end of the container.Preferably, the three-way valve is disposed in proximity to the upperend of the container.

In accordance with another embodiment of the apparatus of the presentinvention, the actuatable valve includes at least three connections, andthe evacuation conduit includes a first evacuation conduit portionconnecting the supply conduit to one of the at least three connections,a second evacuation conduit portion connecting the removal conduit toanother of the at least three connections, and a third evacuationconduit portion connecting the negative pressure side of the pump toanother of the at least three connections, whereby the actuatable valvenormally connects the third evacuation conduit portion to the secondevacuation conduit portion, and upon actuation, the actuatable valveconnects the third evacuation conduit portion to the first evacuationconduit portion.

In a preferred embodiment, the supply conduit includes a constrictiondisposed in the supply conduit distal from the first evacuation conduitportion with respect to the upper end of the container.

In another embodiment, the apparatus includes a supply conduit valvedisposed in the supply conduit distal from the first evacuation conduitportion with respect to the upper end of the container, the supplyconduit valve being normally open but being closable upon actuationduring the elimination of the gases.

In accordance with another embodiment of the apparatus of the presentinvention, the apparatus includes a gas separator in the removalconduit, the gas separator including a gas level indicator forindicating a predetermined level of gas in the gas separator. In apreferred embodiment, the gas separator comprises a chamber having apredetermined cross-sectional area, an inlet proximate to the lower endof the container, and an outlet distal from the lower end of thecontainer, the cross-sectional area of the chamber being substantiallygreater than the area of the removal conduit whereby the flow velocitythrough the chamber is substantially lower than the flow velocitythrough the removal conduit and gas separation takes place therein.Preferably, the apparatus includes a concentrate dosage pump disposed inthe removal conduit downstream of the gas separator with respect to thecontainer.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described below in greater detail withreference to the detailed description which follows, and which, in turn,refers to the attached drawings, in which:

FIG. 1 is a schematic diagram of a dialysis machine according to theprior art, corresponding essentially to the dialysis machine known asGAMBRO AK 100;

FIG. 2 is a schematic diagram corresponding to FIG. 1 with a deaerationdevice according to the present invention;

FIG. 3 is a schematic diagram corresponding to FIG. 1 showing analternative embodiment of the deaeration device according to the presentinvention;

FIG. 4 is a schematic diagram corresponding to FIG. 1 showing a variantof the embodiment of the present invention according to FIG. 3;

FIG. 5 is a schematic diagram corresponding to FIGS. 3 or 4, providedwith an indicator;

FIG. 6 is a schematic diagram corresponding to FIG. 5 showing analternative embodiment of the present invention; and

FIG. 7 is a schematic diagram corresponding to FIG. 6 but with analternative valve arrangement.

DETAILED DESCRIPTION

A dialysis machine is shown schematically in FIG. 1, correspondingsubstantially to the dialysis machine sold as GAMBRO AK 100. Thedialysis machine comprises a water reservoir 1 with inlet 2 for waterwhich is normally received from a water purification plant (RO-unit,reverse osmosis).

The water reservoir 1 contains a heating coil 3 which warms the water toa suitable temperature, usually about 37° C. An outlet 4 is connectedthrough a particle filter 5 to a primary conduit 6 for preparation ofthe dialysis solution.

A first branch conduit 7 supplies A-concentrate from a container 8 bymeans of a suction nozzle 9 inserted in the container, a conduit 10 anda dosage pump 11. The A-concentrate is mixed with water in the conduit 6and is supplied to a mixing chamber 12 where homogenisation of themixture takes place. Thereafter, the mixture passes a conductivity meter13 where the conductivity of the mixture is determined. The conductivitymeter 13 controls the dosage pump 11 so that a predeterminedconductivity is attained. Normally, the A-concentrate is dilutedapproximately in the proportion of about 1:34.

A second branch conduit 14 is located downstream of the conductivitymeter 13, which conduit supplies concentrated bicarbonate orB-concentrate. The thus obtained dialysis solution passes through athrottle valve 15 and further to an expansion chamber 16 and a powerfulpump 17. The dialysis solution is fed from the pump 17 to a bubblechamber 18 and a second conductivity meter 19. The increase of theconductivity with respect to the conductivity meter 13 is determined bythe conductivity meter 19 and the difference signal regulates a dosagepump 20 for bicarbonate concentrate.

The throttle arrangement 15 and the pump 17, together with the expansionchamber 16, form a gas eliminator. Downstream of the throttlearrangement 15, the pressure is relatively low; i.e., around -600 mmHg;and any gas in the solution is released, which is assisted by theexpansion chamber 16. The released gas collects in bubbles and passesthrough the pump 17 to the bubble chamber 18. The received bubbles riseto the upper part of the chamber 18 and are removed at approximatelyatmospheric pressure.

Bicarbonate concentrate is prepared in the above-depicted dialysismachine in situ by use of a cartridge containing bicarbonate powder. Thecartridge 21 is connected to a particular cartridge holder 22 equippedwith swinging arms 23 and 24, as is described in greater detail inEuropean Patent No. 278,100. The cartridge 21 is connected in a circuitwhich runs from the water reservoir 1 through a suction nozzle 25inserted in the water reservoir, a conduit 26 and a throttle arrangement27 to the upper arm 23 of the cartridge holder 22. The upper arm 23 isconnected to the upper end of the cartridge 21 by means of a spike. Thelower end of the cartridge is, in a similar manner, connected to thelower arm 24 and communicates further through a particle filter 28 and aconduit 29 with the dosage pump 20 for bicarbonate concentrate.

The dialysis machine can also be used for B-concentrate in liquid formby swinging the arms 23 and 24 to a shunt conduit 30, with the suctionnozzle 25 being placed in a container for B-concentrate in a mannersimilar to that of the suction nozzle 9.

In order to initially wet the powder in the cartridge 21, the dialysismachine is provided with a priming arrangement in the form of a conduit32 and a valve 31. The conduit 32 is connected between the lower end ofthe cartridge, preferably between the filter 28 and the pump 20, and theprimary conduit 6 downstream of the throttle arrangement 15 where asubstantial vacuum is present (e.g., about -600 mmHg).

Priming takes place by placing a bicarbonate cartridge 21 in the holder23, 24, 22, as shown in FIG. 1, and opening valve 31. In this manner, asubstantial vacuum is applied to the cartridge 21 which draws air out ofthe lower end of the cartridge until the pressure in the cartridge is inthe order of about -600 mmHg.

At the same time, water is drawn from the water reservoir 1 throughconduit 26 and throttle arrangement 27 into the upper end of thecartridge. By means of the throttle arrangement 27, it is ensured thatlow pressure can be established in the cartridge before water flows inthrough arm 23. Thereafter, the cartridge is filled from above withwater which is drawn through the powder in the cartridge 21 andeventually reaches the outlet in the arm 24. This condition is detectedby the conductivity meter 19, whereupon valve 31 is closed.

Concentrate pump 20 is operated during the entire process. Theconcentrate pump 20 now receives liquid-based concentrate from thecartridge 21. A closed circuit has thus been created from the waterreservoir 1 through the conduit 26, the cartridge 21 and the conduit 29to the pump 20.

During the above-mentioned process, a certain quantity of air will havebecome trapped in the upper end of the cartridge in a space 33. However,the water level is above the level of the bicarbonate powder 34 so thatthe powder is constantly wet. During operation, bicarbonate concentrateis removed through the concentrate pump 20. Due to the closed circuit,as much water is supplied to the upper end of the cartridge as isremoved from its lower end. The supplied water dissolves the bicarbonatepowder and a substantially saturated solution is formed in thecartridge. When the solution is saturated, dissolution ceasesautomatically.

Since the cartridge 21 is included in a closed circuit, the gas in thespace 33 remains entrapped and cannot migrate anywhere. This is not adisadvantage and does not lead to any damage.

In the event that a slight vacuum is present in the cartridge 21, anyleak in the connection between the cartridge 21 and the upper arm 23 canresult in an increase in the gas volume in the space 33.

The gas volume can also increase by means of gas accompanying the waterfrom the water reservoir 1 through the conduit 26 to enter the cartridge21.

At high ambient temperatures the sodium bicarbonate solution in thecartridge can to a certain extent decompose to carbon dioxide and sodiumcarbonate (soda). Such carbon dioxide gas can also collect in the space33 and increase the confined gas volume.

The gas volume in the space 33 is only harmful if it becomes too greatand forces the water level below the level of the powder 34. In thatcase there is a risk that the concentrated, substantially saturatedsolution which is removed through the outlet in the arm 24 can contain acertain quantity of gas. The cartridge may even run dry, whereby a largequantity of gas will exit through the outlet 24. This condition cancreate an alarm. If the cartridge runs dry, it must normally bereplaced, which can thus cause an interruption in operation.

In accordance with the present invention, it is proposed to provide thedialysis machine with a valve with which the gas volume in the space 33can be reduced, particularly if it shows a tendency to increase and tobecome far too great, i.e. drop below the level of the powderconcentrate 34.

A first embodiment of the present invention is shown in FIG. 2. Athree-way valve 40 which normally connects the upper end of thecartridge 21 to the water reservoir 1 is placed in the conduit 26. Inits second, activated position, however, the valve 40 connects the upperend of the cartridge 21 to a conduit 41 which leads to a substantialvacuum downstream of the throttle arrangement 15, i.e. to the conduit32.

When the valve 40 is switched over, the air in the upper end of thecartridge 21 is drawn through the valve 40, the conduit 41 and theconduit 42 to the pump 17 and is separated in the subsequent bubblechamber 18 (see FIG. 1). By arranging the valve 40 as close as possibleto the cartridge 21, only a small quantity of water has first to flowthrough the conduits 41 and 32 before the air is drawn out. In thismanner, a substantial vacuum is established in the cartridge 21.

When the valve 40 is returned to its initial position, the vacuum in theupper end of the cartridge 21 will result in water being drawn inthrough the conduit 26 from the water reservoir 1, partially filling thespace 33 in order to equalise the vacuum.

In this manner, the air-filled space 33 can be substantially halved withthe help of a vacuum of about a half atmosphere. Since the valve 40 islocated close to the inlet of the cartridge, the effect of the pressurereduction and subsequent pressure equalisation with water will be asgreat as possible. It is possible to repeat this process several times,for example 3 times in the course of one minute.

This deaeration of the cartridge 21 can occur at repeating timeintervals during dialysis treatment, for example in connection with aregularly repeating calibration of the ultrafiltration sensor in thedialysis machine, which normally occurs at 30-minute intervals. Thedeaeration may result in a conductivity alarm since the large quantityof gas which flows through the conduit 32 and pump 17 can result in theflow in the primary conduit 6 being affected to such a degree that thealarm limits are exceeded. Should the machine be in its calibrationmode, however, the alarm can be suppressed.

The embodiment shown in FIG. 2 has a minor drawback in that any leakagein the valve 40 between the conduit 26 and the conduit 41 can disruptthe functioning of the dialysis machine. One embodiment of the presentinvention in which this drawback is overcome is shown in FIG. 3. In thisembodiment the three-way valve 50, which corresponds to the three-wayvalve 40 in the embodiment according to FIG. 2, is placed in the conduit32 between the priming valve 31 and the connection to conduit 29.

The deaeration valve 50 is thus connected to the valve 31 by means of aconduit 51 and to the conduit 29 through a conduit 52. The valve 50connects the conduit 51 to the conduit 52 in its normal position. In itsactivated position the valve 50 connects the conduit 51 to a deaerationconduit 53 which is connected in the conduit 26 between the throttlearrangement 27 and the inlet to the cartridge 21.

By means of this connection, it is ensured that no substantial pressuresare present across the deaeration valve 50 during normal operation. Thevalve 31 isolates the system from the substantial vacuum in conduit 32.

The deaeration takes place by switching the deaeration valve 50 to itsactivated position, whereafter the valve 31 is opened. In this manner, asubstantial vacuum arises in the conduit 53 through the valve 50, theconduit 51, the valve 31 and the conduit 32. A suction pressure thusarises in the conduit 26 at the connection to the conduit 53. Air willthus be drawn from the upper end of the cartridge 21. At the same time,water flows from the water reservoir 1 by means of the conduit 26 andthe throttle arrangement 27 to the conduit 53. Due to the throttlearrangement 27, there is still, however, a substantial vacuum in theupper end of the cartridge 21. Thereafter, the valve 31 is closedwhereby water flows from the water reservoir 1 through the conduit 26,the throttle arrangement 27 and to the upper end of the cartridge 21 toequalise the vacuum therein. The valve 31 can thereafter be opened for asecond deaeration cycle if so desired.

An alternative method of operating the deaeration arrangement accordingto FIG. 3 is the following. Firstly, the valve 50 is switched to itsactivated position, whereafter the valve 31 is opened and a substantialvacuum is established in the upper end of the cartridge 21. Thereafter,the valve 50 is switched to its normal position whereby the substantialvacuum is diverted to the conduit 29 which is connected to the lower endof the cartridge 21. In this manner, water flows from the waterreservoir 1 through the conduit 26, the throttle arrangement 27 and intothe upper end of the cartridge 21. The valve 50 is thereafter switchedback to its activated position and further gas is withdrawn from theupper end of the cartridge 21 by means of the conduit 53. This processis repeated one or more times. Finally, normal operation is resumed byswitching the valve 50 to its normal position and closing the valve 31.The advantage of this method is that the powder in the cartridge 21 isagitated and any gas bubbles which adhere to the powder are loosened andrise to the upper end of the cartridge 21. At the same time, any channelformations in the powder in the cartridge can be avoided.

A combination of the two above-described methods can also be used inwhich the valve 13 is closed between each switching action of the valve50 to permit equalisation of the pressure in the cartridge 21 by meansof the conduit 26 before the vacuum is applied to the lower end of thecartridge by means of the conduit 29.

An alternative embodiment to that of FIG. 3 is shown in FIG. 4. Sincethe throttle arrangement 27 is normally positioned very close to theinlet to the cartridge 21, it can be difficult to connect the conduit 53downstream of the throttle arrangement 27.

In the embodiment which is shown in FIG. 4, the conduit 63 from thevalve 60 has been connected to the conduit 26, and the throttlearrangement 27 has been removed. A normally open valve 64 is connectedin conduit 26 between the water reservoir 1 and the connection to theconduit 63. The valve 60 is connected to the valve 31 by means of aconduit 61 and is connected to the conduit 29 by means of a conduit 62.

During connection of the valve 60, the valve 64 is closed, and in thismanner water cannot be withdrawn from the water reservoir throughconduit 26 to conduit 63. Otherwise, the operation is the same as forthe operation according to the embodiment of FIG. 3. In the embodimentof FIG. 4, operation of the throttle arrangement 27 is replaced byoperation of valve 60.

As has been stated above, the deaeration valves 40, 50, 60 can beactivated on those occasions when it is desired to deaerate thebicarbonate cartridge 21. Such deaeration can take place regularly in30-minute intervals during the dialysis treatment, when the normaldialysis treatment is interrupted for a calibration step. It is alsopossible to provide the dialysis machine with the capability of manualinitiation of deaeration. This can occur should a nurse or other userdiscover that the water level has dropped below the level of the powder34 in the cartridge 21, or when the trapped volume of gas becomes toogreat.

It is also feasible to provide the holder 22 with an arrangement whichsenses if the water level drops below the level of the indicator. Suchan indicator could be a load-cell 65 as illustrated in FIG. 4. In FIG. 4there is additionally shown an electronic device 66 or microprocessorwhich controls the function of the valves, as indicated by dashed linesin FIG. 4. Device 66 can be adapted to control or indicate whendeaeration is required, for example at regular time intervals oraccording to signals from an indication device or upon demand from auser.

A further indication arrangement is shown in FIG. 5. The embodimentaccording to FIG. 5 is provided with the same valves and conduits as theembodiment according to FIG. 4. In addition, the conduit 29 whichconnects the outlet of the cartridge 21 to the dosage pump 20 isprovided with a deaeration indicator 70 in the form of a gas separationchamber 71.

The chamber 71 is provided with an inlet 72 connected to the outlet fromthe cartridge 21 through a conduit 73, and to an outlet 74 connected tothe conduit 29 and further to the pump 20. The chamber 71 may bepositioned anywhere along the conduit 29 between the outlet from thecartridge 21 and the dosage pump 20.

The bicarbonate concentrate from the cartridge 21 thus flows to thechamber 71, which has a relatively large cross section. Due to the lowflow velocity in the chamber 71, any gas bubbles in the concentrate areseparated and rise to the upper end of the chamber 71. If thebicarbonate concentrate should contain a large quantity of small gasbubbles, such as can be the case at high ambient temperatures, theconfined gas volume in the chamber will increase. When the gas volume orthe water level in the chamber 71 reaches an indicator 75, a signal isemitted which indicates that deaeration is required.

If the cartridge 21 runs dry so that the space 33 increases greatly involume and the risk arises that gas will be drawn out together with theconcentrate, the gas which accompanies the concentrate will quickly fillthe chamber 71 so that the level indicator 75 is activated.

The chamber 71 preferably has a volume which is large enough such thatthe quantity of concentrate which is accommodated beneath the indicator75 is sufficient for, for example, several minutes' treatment; i.e.about 50 ml. If the cartridge has run dry, the dialysis treatment canthus continue for several minutes in anticipation of a suitable occasionfor deaeration.

When the level indicator 75 registers that deaeration is required, thevalves 60, 31 and 64 are activated as described above in connection withthe embodiment according to FIG. 4. In addition, the chamber 71 isprovided with a conduit 76 which connects the upper gas-filled end ofthe chamber with the conduit 61 between the valve 60 and the valve 31.Furthermore, the conduit 66 is provided with a throttle arrangement 77.When the deaeration cycle is activated by activating the valve 60 andthe valve 31 is opened, the upper end of the chamber 71 will thus beevacuated by the conduit 76, conduit 61, the valve 31 to the conduit 32.When the water level in the chamber 71 has risen such that water fillsthe conduit 76 and reaches the throttle arrangement 77, the flow throughthe conduit 76 will be very small. At termination of the deaerationcycle, the chamber 71 will therefore be substantially full of liquid anda new monitoring cycle can be initiated by means of the chamber 71.

During normal operation, bicarbonate concentrate flows from thecartridge 21 through conduit 73 and chamber 71 to the conduit 29 and theconcentrate pump 20. It has been shown that the conductivity measurementin the conductivity meter 19 attains considerably smaller fluctuationsdownstream of the connection of chamber 71. The reduction of thefluctuations is already noticeable at a room temperature of 20° C. andbecomes even more marked at room temperatures in the order of 30° C.,something which can arise in warm countries.

One explanation for the above-mentioned fluctuations and the decreasewhen the chamber 71 is connected can be the following. At higher ambienttemperatures, carbon dioxide gas is formed in the cartridge 21 at thesame time as dissolution of the powder, or during the periodsubstantially saturated concentrate is in the cartridge 21 before beingfed through the outlet to the conduit 29. As the concentrate is fed out,the smallest bubbles, which do not adhere to adjacent salt particles,accompany the concentrate. The quantity of gas bubbles in the exitingconcentrate varies stochastically. At higher temperatures, the mixtureis greater and, as a result, so too is the variation of the mixed gasbubbles. The pump 20 is a metering pump which pumps a predeterminedquantity of concentrate per revolution or fraction of a revolution.Since the concentrate is, however, diluted with gas bubbles, differentquantities of sodium bicarbonate will pass through the pump depending onthe intermixed quantity of gas. The intermixed quantity of gas isthereafter effectively separated in the bubble chamber 18. Theconductivity meter 19 is thus subjected to a varying concentration wherethe variation depends on the quantity of intermixed gas bubbles duringthe passage of the pump 20. The more gas bubbles which are intermixed,the lower the concentration of the bicarbonate becomes.

By introducing a bubble separator or gas separator 71 before themetering pump 20, it is ensured that the pump 20 always pumps saturatedconcentrate which is not diluted with gas bubbles. Consequently, thefeeding of bicarbonate to the primary conduit 60 will be very consistentand without fluctuations, and as such the conductivity meter 19 emits avery constant signal.

A further embodiment of the present invention is shown in FIG. 6 whichis a variation of the embodiment according to FIG. 5. The switchingvalve 60 has in this case been replaced by a simple valve 80 and theconduit 62 has been omitted.

In this embodiment, priming of the cartridge 21 takes place by openingthe valve 31 while the valve 80 is closed and the valve 64 is in itsnormal open position. In this manner, a substantial vacuum is obtainedin the cartridge 21 through conduit 73, the chamber 71, the conduit 76,the throttle arrangement 77, the conduit 81, the valve 31 and theconduit 32. Water flows from the water reservoir 1 through valve 64 andthe conduit 26 and the throttle arrangement 27 to the upper end of thecartridge 21. Water is thus introduced into the upper portion of thecartridge 21 and is withdrawn from the lower portion and the conduit 73and fills the chamber 71. At the same time, the pump 20 is running, thuscausing the liquid to flow through the outlet 74 to the conduit 29 andthe pump 20. Simultaneously, the air in the upper end of the chamber 71is withdrawn through conduits 76 and 81. When the entire chamber 71 isfilled with concentrate, the conduit 76 is filled up to the throttlearrangement 77 with concentrate. When liquid reaches the throttlearrangement 77, the pressure drop over the throttle arrangement fallssubstantially, which is sensed by a pressure sensor 84 arranged inconnection with the conduit 76. The pressure sensor 84 indicates thatpriming has been achieved and the valve 31 is closed. The cartridge 21is thereafter refilled from the water reservoir 1 through conduit 26 andthe throttle arrangement 27 until approximately atmospheric pressure isattained in the cartridge 21, (a slight vacuum is normally present inthe cartridge 21).

When the level indicator 75 registers that deaeration is necessary, thisis attained by opening the valves 80 and 31 at the same time that thevalve 64 is closed. Otherwise, the function is identical to that whichhas been described in connection with FIG. 5.

In FIG. 6 it is shown that the separation chamber has been provided witha particular conical inlet 85 which faces upwardly. The concentrate thusflows upwardly through the inlet 85 with continuously diminishingvelocity. The surface at the upper end of the inlet 85 is as large asthe ring surface exterior of the upper end of the outlet so that theconcentrate flows around the edge and continues downwardly withoutincreasing the flow velocity. The flow velocity decreases further duringthe transport downwardly to the outlet 74. This flow pattern isfavourable for separating gas bubbles in the flowing liquid.

An alternative embodiment is shown in FIG. 7 in which the valve 80 isconnected directly to the conduit 32 instead of through valve 31. Anevacuation conduit 86 connects the conduit 32 to the valve 80 andfurther to the conduit 63. In this manner, the valves 80 and 31 can becontrolled totally independently of each other.

During normal priming in the embodiment according to FIG. 7, the valve64 is first closed while the valve 31 is open. In this manner, it isensured that a substantial vacuum is attained in the cartridge 21 beforewater is supplied through the opening of the valve 64. In this manner,an improved filling of the cartridge during priming is attained.

The present invention has been described above in connection withpreferred embodiments of the invention, suitable for use in the dialysismachine known as GAMBRO AK 100. The invention can, of course, be adaptedto other types of dialysis machines, for example where an overpressureis present in the bicarbonate cartridge 21.

The present invention has also been described in connection with use ofthe internal feed pump for the elimination of the gases. Naturally, aseparate pump can be used if this should be desired.

The gas separation chamber performs two functions; on the one hand itserves as an indicator for when the cartridge requires gas eliminationand, on the other hand, it performs deaeration of the concentrate whichis obtained from the cartridge so that a more accurate dosage can beobtained in the dosage pump and noise can be eliminated in theconductivity meter. The latter-mentioned property can also be performedseparately without the chamber being used for indication, for example byelimination of gases occurring time-dependently, for example every halfhour.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

What is claimed is:
 1. Apparatus for the elimination of gases from acontainer including an upper end and a lower end for preparing aconcentrate of a powder in water, said apparatus comprising a supplyconduit for supplying water to said container, a removal conduit forremoving said concentrate from said container, a pump including anegative pressure side, an evacuation conduit for connecting saidnegative pressure side of said pump with said container, an actuatablevalve disposed in said evacuation conduit whereby upon actuation saidactuatable valve connects said container with said negative pressureside of said pump, wherein said actuatable valve comprises a three-wayvalve normally connecting said supply conduit to said upper end of saidcontainer.
 2. The apparatus of claim 1 wherein said powder comprises abicarbonate powder and said concentrate comprises a dialysis solution.3. The apparatus of claim 1 wherein said three-way valve is disposed inproximity to said upper end of said container.
 4. The apparatus of claim1 including a gas separator in said removal conduit, said gas separatorincluding a gas level indicator for indicating a predetermined level ofgas in said gas separator.
 5. The apparatus of claim 4 wherein said gasseparator comprises a chamber having a predetermined cross-sectionalarea, an inlet proximate to said lower end of said container, and anoutlet distal from said lower end of said container, saidcross-sectional area of said chamber being substantially greater thanthe area of said removal conduit whereby the flow velocity through saidchamber is substantially lower than the flow velocity through saidremoval conduit and gas separation takes place therein.
 6. The apparatusof claim 5 including a concentrate dosage pump disposed in said removalconduit downstream of said gas separator with respect to said container.7. The apparatus of claim 1, further comprising an indicator forindicating when said container includes a predetermined amount of saidgases, and control means for actuating said actuatable valve in responseto said indicator to eliminate said gases from said container. 8.Apparatus for the elimination of gases from a container including anupper end and a lower end for preparing a concentrate of a powder inwater, said apparatus comprising a supply conduit for supplying water tosaid container, a removal conduit for removing said concentrate fromsaid container, a pump including a negative pressure side, an evacuationconduit for connecting said negative pressure side of said pump withsaid container, an actuatable valve disposed in said evacuation conduitwhereby upon actuation said actuatable valve connects said containerwith said negative pressure side of said pump, said actuatable valveincluding at least three connections, and wherein said evacuationconduit includes a first evacuation conduit portion connecting saidsupply conduit to one of said at least three connections, a secondevacuation conduit portion connecting said removal conduit to another ofsaid at least three connections, and a third evacuation conduit portionconnecting said negative pressure side of said pump to another of saidat least three connections, whereby said actuatable valve normallyconnects said third evacuation conduit portion to said second evacuationconduit portion, and upon actuation said actuatable valve connects saidthird evacuation conduit portion to said first evacuation conduitportion.
 9. The apparatus of claim 8 wherein said supply conduitincludes a constriction disposed in said supply conduit distal from saidfirst evacuation conduit portion with respect to said upper end of saidcontainer.
 10. The apparatus of claim 8 including a supply conduit valvedisposed in said supply conduit distal from said first evacuationconduit portion with respect to said upper end of said container, saidsupply conduit valve being normally open but being closable uponactuation of said actuatable valve during said elimination of saidgases.
 11. Apparatus for the elimination of gases from a containerincluding an upper end and a lower end for preparing a concentrate of apowder in water, said apparatus comprising a supply conduit forsupplying water to said container, a removal conduit for removing saidconcentrate from said container, a pump including a negative pressureside, an evacuation conduit for connecting said negative pressure sideof said pump with said container, a first actuatable valve disposed insaid evacuation conduit, whereby upon actuation said first actuatablevalve connects said container with said negative pressure side of saidpump, and a second actuatable valve connecting said supply conduit tosaid upper end of said container when said first actuatable valve isclosed.